PROJECT ABSTRACT Opioid abuse is a public health epidemic in the United States, and naloxone plays a critical role in opioid overdose prevention. To expand naloxone's availability and use by both emergency medical services (EMS) personnel and community bystanders (CB), states have enacted a variety of policy and regulatory responses, but we have little empirical evidence for how the the implementation of specific policies or policy combinations influence the sources, methods, and saturation of naloxone use across communities. This project will compile a comprehensive database of relevant state policies and provisions aimed at increasing EMS or CB use of naloxone and employ a modified Delphi approach to develop composite state policy scales that characterize the strength of state 1) EMS naloxone policy implementation, and 2) CB naloxone policy implementation. We will then use these developed composite measures to assess the extent to which strength of EMS naloxone policy implementation is associated with increased use of naloxone by EMS personnel of different certification levels and of different routes of administration as well as the extent to which strength of CB naloxone policy implementation is associated with increased pharmacy dispensation of naloxone to the public. Finally, we will explore whether the simultaneous presence of different types of EMS and community bystander naloxone policies interact to influence the use of naloxone by EMS or laypersons. By accounting for variation in the strength of policy implementation across states and over time, findings will inform public health and policy by improving scientific understanding of the key policy elements that promote naloxone access and use within the broader policy environment.